Just found my DC07 is HEPA. Like you, I didn't want that but it was on offer at over £100 off, which made it much cheaper than the non-HEPA version. Had forgotten about that.
Well, you're describing my non-HEPA filter perfectly ;-)
Same on my DC07. However, curiosity just got the better of me, and I levered the cover off. This reveals it is the post-motor filter which is the HEPA filter on my DC07 -- it says so all over it;-) It is stained darker on the filter surface where the main airflow goes into it. This stain comes off on fingers, and I suspect it is material worn off the motor brushes -- looks like that. There are three filter components inside the HEPA filter, and the middle and outlet ones are still bright white. In my DC04 (definately non-HEPA), the post motor filter is much simpler.